The Sarthe () is a river in western France. Together with the river Mayenne it forms the river Maine, which is a tributary to the river Loire.
Its source is in the Orne department, near Moulins-la-Marche. It flows generally southwest, through the following departments and towns:
- Orne: Le Mêle-sur-Sarthe, Alençon
- Sarthe: Fresnay-sur-Sarthe, Beaumont-sur-Sarthe, Le Mans, Sablé-sur-Sarthe
- Maine-et-Loire: Châteauneuf-sur-Sarthe, Tiercé, Angers
Its main tributaries are the Loir and the Huisne from the left, and the Vaige, the Erve and the Vègre from the right.